An internal combustion engine installed on an automotive vehicle or a motorcycle generates heat and noises when the engine is in operation and thus constitutes an important source of heat and noises in the vehicle. The heat and vibrations originating in the internal combustion engine are transferred to the air cleaner and other units and members located in the neighborhood of the engine or structurally connected to the engine. The heat and vibrations transferred to these members and units are liable to impair the performances and lessen the service lives of the members and units. The vibrations transferred to, for example, the casing of the engine or the front engine hood panel may cause these members to resonate and produce noises therefrom. It is thus required to have the engine per se or the structurally or functionally associated members and units provided with sound and heat insulating means. Conventional sound and heat insulating means to meet the purpose are however not fully acceptable.